1. Technical Field
The present invention relates to an image reading apparatus and a semiconductor device.
2. Related Art
An image reading apparatus (scanner and the like) using a contact image sensor, and a copying machine, a combination printer, or the like to which a printing function has been added have been developed. As the contact image sensor used in the image reading apparatus, a configuration of using a photodiode provided on a semiconductor substrate is used.
In the contact image sensor used in the image reading apparatus such as a scanner, multiple pixel units of which each includes one or a plurality of photodiodes are disposed in line in one direction. Thus, a chip shape thereof is a very elongated rectangular shape. Because the length of a long side of the chip is determined by the size of a pixel (photodiode) or the number of pixels, only a method of reducing a short side of the chip is provided in order to reduce the chip size. Various pads (terminals) such as an input pad, an output pad, and a power source pad, and various circuits such as an input and output circuit, a control circuit, and a pixel drive circuit are provided in a region other than an arrangement region of pixel units in the chip. The number of bondings between the chip and a circuit board is desirably small. In order to cause the number of pads to be necessarily the minimum, the pads are arranged in the vicinity of the long side of the chip, and the various circuits are arranged in an empty region between the pads. Accordingly, it is possible to reduce the length of the chip in a short-side direction.
JP-A-2012-134257 discloses a solid state imaging device in which a circuit is disposed between pads, and a signal wiring passes under the pads, and thus it is possible to reduce a chip area.
In a case where only one pair of power source pads is provided in order to reduce the number of pads, a long power source wiring in a long-side direction of a chip is required to be provided in order to supply power to various circuits. However, as the power source wiring becomes farther from the power source pad, the dropped amount of a power source voltage by a resistive component of the power source wiring is increased. Thus, the position of the power source pad or the layout of the power source wiring has a large influence on characteristics of an imaging sensor. In the solid state imaging device disclosed in JP-A-2012-134257, power source pads are provided at both ends of the chip on the long side thereof. Thus, the dropped amount of a power source voltage is large in the vicinity of the center of the chip on the long side thereof, and this may cause the characteristics to be largely degraded. Further, since the signal wiring passes under the pads, there is a problem in reliability of bonding pads or the signal wiring. That is, in the solid state imaging device disclosed in JP-A-2012-134257, the position of the power source pad or the layout of the power source wiring for improving characteristics of an imaging sensor is not totally considered.